Rollup merge of rust-lang#95933 - Urgau:rustdoc-htmldocck-tree-compare, r=GuillaumeGomez

htmldocck: Compare HTML tree instead of plain text html

This PR improves `htmldocck` by comparing HTML trees instead of plain text html in the case of doing a ```@snapshot``` test.

This fix the [CI issue](https://github.com/rust-lang-ci/rust/runs/5964305020?check_suite_focus=true) encounter in rust-lang#95813 where for some unknown reason one of the attributes is not always at the same place.

The code is largely based on https://github.com/formencode/formencode/blob/3a1ba9de2fdd494dd945510a4568a3afeddb0b2e/formencode/doctest_xml_compare.py#L72-L120 which is behind MIT License. The comparison function is straightforward except for the `text_compare` function which does some weird stuff that we may want to simply reduce to a plain old comparison.

r? ``@GuillaumeGomez``

Author: Dylan-DPC

src/etc/htmldocck.py

@@ -285,6 +285,11 @@ def flatten(node):
     return ''.join(acc)
 
 
+def make_xml(text):
+    xml = ET.XML('<xml>%s</xml>' % text)
+    return xml
+
+
 def normalize_xpath(path):
     path = path.replace("{{channel}}", channel)
     if path.startswith('//'):
@@ -401,7 +406,7 @@ def get_tree_count(tree, path):
     return len(tree.findall(path))
 
 
-def check_snapshot(snapshot_name, tree, normalize_to_text):
+def check_snapshot(snapshot_name, actual_tree, normalize_to_text):
     assert rust_test_path.endswith('.rs')
     snapshot_path = '{}.{}.{}'.format(rust_test_path[:-3], snapshot_name, 'html')
     try:
@@ -414,11 +419,15 @@ def check_snapshot(snapshot_name, tree, normalize_to_text):
             raise FailedCheck('No saved snapshot value')
 
     if not normalize_to_text:
-        actual_str = ET.tostring(tree).decode('utf-8')
+        actual_str = ET.tostring(actual_tree).decode('utf-8')
     else:
-        actual_str = flatten(tree)
+        actual_str = flatten(actual_tree)
+
+    if not expected_str \
+        or (not normalize_to_text and
+            not compare_tree(make_xml(actual_str), make_xml(expected_str), stderr)) \
+        or (normalize_to_text and actual_str != expected_str):
 
-    if expected_str != actual_str:
         if bless:
             with open(snapshot_path, 'w') as snapshot_file:
                 snapshot_file.write(actual_str)
@@ -430,6 +439,59 @@ def check_snapshot(snapshot_name, tree, normalize_to_text):
             print()
             raise FailedCheck('Actual snapshot value is different than expected')
 
+
+# Adapted from https://github.com/formencode/formencode/blob/3a1ba9de2fdd494dd945510a4568a3afeddb0b2e/formencode/doctest_xml_compare.py#L72-L120
+def compare_tree(x1, x2, reporter=None):
+    if x1.tag != x2.tag:
+        if reporter:
+            reporter('Tags do not match: %s and %s' % (x1.tag, x2.tag))
+        return False
+    for name, value in x1.attrib.items():
+        if x2.attrib.get(name) != value:
+            if reporter:
+                reporter('Attributes do not match: %s=%r, %s=%r'
+                         % (name, value, name, x2.attrib.get(name)))
+            return False
+    for name in x2.attrib:
+        if name not in x1.attrib:
+            if reporter:
+                reporter('x2 has an attribute x1 is missing: %s'
+                         % name)
+            return False
+    if not text_compare(x1.text, x2.text):
+        if reporter:
+            reporter('text: %r != %r' % (x1.text, x2.text))
+        return False
+    if not text_compare(x1.tail, x2.tail):
+        if reporter:
+            reporter('tail: %r != %r' % (x1.tail, x2.tail))
+        return False
+    cl1 = list(x1)
+    cl2 = list(x2)
+    if len(cl1) != len(cl2):
+        if reporter:
+            reporter('children length differs, %i != %i'
+                     % (len(cl1), len(cl2)))
+        return False
+    i = 0
+    for c1, c2 in zip(cl1, cl2):
+        i += 1
+        if not compare_tree(c1, c2, reporter=reporter):
+            if reporter:
+                reporter('children %i do not match: %s'
+                         % (i, c1.tag))
+            return False
+    return True
+
+
+def text_compare(t1, t2):
+    if not t1 and not t2:
+        return True
+    if t1 == '*' or t2 == '*':
+        return True
+    return (t1 or '').strip() == (t2 or '').strip()
+
+
 def stderr(*args):
     if sys.version_info.major < 3:
         file = codecs.getwriter('utf-8')(sys.stderr)